1. FIELD OF THE INVENTION
The present invention relates to lead frames for integrated circuits, and more particularly to lead frames for glass-encapsulated integrated circuits.
2. PRIOR ART
Glass-encapsulated integrated circuits are conventionally assembled by stamping a strip of Alloy 42 into a lead frame having a plurality of leads, then attaching the lead frame to a ceramic substrate coated with glass, then fixing an IC (integrated circuit) chip to the assembly, and finally connecting the tips of the inner ends of the leads of the lead frame to electrodes of the IC chip with wires of aluminum, normally by an automatic bonder. It is important that the tips of the inner ends of the leads of the lead frame which is attached to the ceramic substrate be located in predetermined positions. If the tips are displaced out of position due to deformations, the aluminum wires will not be properly bonded to the displaced tips, and the resulting IC device will be useless. As shown in FIG. 1 of the accompanying drawings, an ordinary conventional lead frame has thin leads which extend toward the center of the frame and are supported only at their outer ends, provides a construction which is mechanically weak and susceptible to deformation. The leads can be easily deformed due to residual stresses created when the lead frame is stamped out of a raw material, or else due to rough handling during subsequent assembling operations. At the same time, as more and more electronic functions are performed by IC, the lead frame must have an increased number of leads which are increasingly thinner and longer and which are hence more easily subject to deformations.
One way to reduce such deformations is disclosed in U.S. Pat. No. 4,137,546 to J. M. Frusco. In this patent a lead frame is shown in which the tips of the inner ends of the leads are spaced apart at intervals by separate tabs. However, these tabs cannot prefectly prevent the leads from being deformed. More specifically, when one of the tabs is subjected to an external force, all of the leads that are connected to that tab will be deformed. In addition, the tabs must be broken off by being bent in a subsequent operation which, however, cannot be mechanically performed due to various difficulties.
It is an object of the present invention to provide a lead frame having leads arranged to resist deformation so that aluminum wires can be reliably connected thereto by an automatic bonder.